Mercaptothiazines as sulfur-corrosion inhibiting agents



Patented Dec. 2, 1952 UNITED STATES PATENT 2,620,303 9 F F! C E 2,620,303 MERCAPTOTHIAZINES AS SULFUR- C-ORROSION INHIBITING AGENTS Delaware No Drawing. Application July 9, 1949, Serial No. 103,936

The present invention relates to lubricating oils compounded with active sulfur-containing compounds such as metal salts of thiophosphate's, which compounded oils are severely corrosive to silver and like metals, and to the prevention of such sulfur attack on silver by incorporatin'gin said severely corrosive compounded oils certain protective agents such as 2-mercapto-4,6,6-trimethyl thiazine.

Of the various lubricating oil compounding agents, many of the most effective are compounds containing sulfur. For example, aliphatic polysulfides, metal salts of organo thiophosphates, etc. are highly effective oxidation inhibitors; and sulfurized olefins, xanthate esters and the like are excellent extreme pressure agents. Unfortunately, oils compounded with such active sulfur-containing compounds are severely corrosive to silver and like metals. The deleterious action involves a direct attack of the metals by sulfur, resulting in a rapid darkening of the metal surfaces and formation of sulfides and the subsequent sloughing off of the sulfides during engine operation. Thus, there is a considerable loss of bearing metal and a pitting of'bearing surfaces. This sulfur attack may be designated as sulfur corrosion, as distinguished from corrosion caused by the action of acids and peroxides which are found as products of oxidation of lubricating oils, particularly highly refined lubricating oils. This latter type of corrosion,-which may be called oxidation corrosion or acid corrosion, adversely affects such hard metal alloys as cadmium-silver, copper-lead, etc., but does not seriously affect silver or bronze. Such oxidation corrosion is usually minimized by the presence of oxidation inhibitors, which reduce the formation of the corrosive acids and peroxides.

It is apparent that in spite of the long desire to lubricate silver bearings with lubricants compounded with active sulfur compounds, it has been impractical to do so in view of the aforementioned severe corrosivity to silver.

Therefore, it isan object of this invention to provide a non-silver-corrosive lubricant containing active sulfur compounds.

In the attainment of this object, the present invention concerns the combination of a lubricant compounded with active sulfur compounds, which compounded lubricant is severely corrosive to silver and a silver protective agent which greatly minimizes the attack on silver by sulfur of the compounded lubricant but without adversely affecting the desired functioning of the sulfur compound.

Heretofore, in the lubrication of engines having silver metal wearing surfaces, for example in certain railroad diesel engines which use silver wrist-pin bushings, it has been difficult to prevent sulfur attack of the silver surfaces. Because the silver surfaces (e. g., the silver wrist-pin bush- 7 Claims. (Cl. 252-4237) ings) are susceptible to attack by the sulfur of the sulfur-containing lubricating oil additive, there has been a tendency to eliminate highly effective sulfur-containing additives from the diesel lubrieating oils, thereby losing the remarkable benefits of these additives. As noted hereinabove, certain highly effective lubricating oil anti-oxidants contain sulfur which is corrosive to silver. These effective anti-oxidants have not been used in diesel engines containing silver wrist-pin bushings without sulfur attack of the silver. Alternative practices have been to eliminate the sulfur-containing additives from the oil, allowing the oil to deteriorate more rapidly through oxidation; or the sulfur-containing additives have been included in the oil formulation, with the resulting sulfur corrosion of the silver wrist-pin bushings. Silver is also used in wearing surfaces in aircraft engines, but because of the presence of the silver, the highly effective sulfur-containing aviation oil additives are not used. Now, however, by using the compounds of this invention, lubricating oils compounded with sulfur-containing additives can be used in diesel oils, aviation oils, and any other oils where sulfur corrosion of metals is a problem.

It is of extreme advantage to be able to use a lubricant composition which is effective not only in inhibiting oxidation corrosion but is also effective in preventing sulfur attack on metals. In railroad oils, for example, it has been a handicap to use lubricants which inhibit corrosion resulting from oxidation products but permitting unhampered attack on metals by compounds having active sulfur present. I While the outstanding advantages of the cooperative action of the silver protective agents in otherwise severely corrosive lubricants containing sulfur compounds is particularly apparent in heavy-duty motor oils, the inventive combination finds application in turbine oils, gear oils, such as for use in hypoid gears, cutting oils, soluble oils, greases, etc.

The action of the silver protective agents cannot be explained on any simple basis, since their apparent effect appears anomalous; on the one hand, the protective agents prevent destructive attack of the sensitive metal by active sulfur compounds; .but, on the other hand, they do not interfere with the functioning of extreme pres sure agents which are believed to act by reaction with the metal surface.

The silver protective agents of this invention are 2-thiothiazines. The simplest member of this class of compounds is z-mercaptothiazine. Also included are the derivatives of 2-mercaptothiazine, wherein the mercapto-hydrogen may be replaced by a hydrolyzable group and wherein there may be substituents on the ring carbon atoms.

The hydrolyzable group is one which may reradicals (e. g., cyclohexylamide radical), and

organic carboxyl and thionyl radicals (e. g., benzoic and diethyl dithiocarbonyl radicals).

In z-thiothiazine, the hydrogen atoms of the ring may be substituted by short-chain saturated and unsaturated aliphatic radicals (e. g., methyl, ethyl, propyl, butyl, octyl, ethenyl, propenyl, butenyl, octenyl, etc.)

It is preferred that there should be not more than 4 substituents on the ring and that each substituent contain not more than 4 carbon atoms. Furthermore, it is preferred that the substituents on the ring have a total of not more than 16 carbon atoms.

By short-chain aliphatic radicals is meant aliphatic radicals containing not more than 8 carbon atoms.

Examples of Z-thiothiazines are: 2-mercapto- 4,6,6-trimethylthiazine; the zinc salt of 2-mercapto 4,6,6 trimethylthiazine; 2 mercapto- 1,3 dihydrothiazine; 4,6,6 trimethylthiazine z-cyclohexyl sulfenamide; 2'-mercapto-2,4,1-trimethylthiazine; 2-mercapto-4-methylthiazine; 2- mercapto 4 ethylthiazine; 2 mercapto 4,6- dimethyl-thiazine; and 2-mercapto-4-isobutenyl- 6,6-dimethylthiazine. Further examples of 2 thiothiaz'ine include the reaction products obtained by reacting Z-thiothiazine with the following: carboxylic acids, alpha-beta unsaturated ketones, esters, olefins, nitriles, sulfonyl halides, organometallic compounds, anhydrides, ethylene oxides and acyl halides.

The 2-thiothiazines embraced in this invention vary in effectiveness as silver protective agents. Because of the greater effectiveness obtained, it is preferred to use 2-mercapto4,6,6- trimethylthiazine.

The 2-thiothiazines embraced in this invention vary in effectiveness as silver protective agents. Some of the compounds, for example, are effective when used in amounts as low as 0.001% (by weight of total composition). Certain of the compounds have only limited solubility in the lubricating oiland are effective at that solubility. All of the compounds having sufficient solubility are effective when they are used in amount as great as 5.0%. However, it is preferred that the compounds of this invention be used in amounts sufficient substantially to reduce the corrosion of silver. For example, it is preferred to use amounts of from 0.05 to 1.5%. The major portion of the lubricating composition of this invention is the base oil.

Suitable base oils include a wide variety of lubricating oils such as naphthenic base, paraffin base, and mixed base mineral oils, other hydrocarbon lubricants, e. g., lubricating oil derived from coal products, and synthetic oils, e. g., alkylene polymers (such as polymers of propylene, butylene, etc., and mixtures thereof), alkylenroxide-type polymers, dicarboxylic acid esters and liquid esters of acids of phosphorus. Synthetic oils of the alkylene-oxide type polymer which may be used include those exemplified by the alkylene oxide polymers (e. g., propylene oxide polymers) and derivatives, including alkylene oxide polymers prepared by polymerizing alkylene oxides, e. g., propylene oxide, in the presence of water or alcohols, e. g., ethyl alcohol, and esters of alkylene-oxide type polymers, e. g., acetylated propylene oxide polymers prepared by acetylating propylene oxide polymers containing hydroxyl groups.

Synthetic oils of the dicarboxylic acid ester type include those which are prepared by esterifying' such dicarboxylic acids as adipic acid, azelaic acid, suberic acid, sebacic acid, alkenyl succinic acid, fumaric acid, maleic acid, etc., with alcohols such as butyl alcohol, hexyl alcohol, 2- ethyl-hexyl alcohol, dodecyl alcohol, etc. Examples of dicarboxylic acid ester synthetic oils include di-butyl adipate, di-hexyl adipate, di-2- ethyl-hexyl sebacate, dim-hexyl fumarate polymer, etc.

Synthetic oils of the type of liquid esters of acids of phosphorus include the esters of phosphoric acid, e. g., tricresyl phosphate; the esters of phosphonic acid, e. g., di-ethyl ester of decane phosphonic acid (or other such esters as obtained by reacting alkyl phosphonyl chlorides with hydroxyl-containing compounds such as phenols and aliphatic alcohols, and with olefin oxides such as propylene oxide, as described in Jensen et al., U. S. patentapplication No. 86,856)

The improved lubricant of the present invention is used wherever elemental sulfur or sulfur compounds having active sulfur present attackmetals and are severly corrosive" to metals which are being lubricated. Thus, as a result of the present invention, lubricants which normally are "severely corrosive to metal parts due.

to attack by sulfur or active sulfu compounds may now be used without fear of corrosion by incorporating therein the present protective agents. Severely corrosive is defined as that corrosion which causes a weight los greate than 30 milligrams in the silver strip test noted hereinbelow.

In order to evaluate the agents of this invention for inhibiting corrosion due to active sulfur, a silver strip corrosion test" was made on numerous agents of this invention. Thi silver strip corrosion test was performed as follows:

A silver metal strip having the dimensions of 2 inches by inch by inch was first cleaned with a. wire brush until the strip was highly polished. The strip was weighed and the weight recorded. This highly polished silver strip was then placed in a 600 milliliter beaker in such a manner that the strip was completely immersed when 300 grams of the oil being tested was poured into the beaker. The oil was stirred at a temperature of 300 F. for 20 hours, at which time anide wash was noted and recorded as the weight,

loss due to corrosion by the sulfur compound.

The agents of this invention are especially effective as protective agents for silver. However, the protective agents of this invention are also effective in protecting other sulfur sensitive metals from sulfur attack. Such other sulfursensitive metals include copper, aluminum and alloys of copper and aluminum. 1

' As illustrative of various sulfur-containing extreme pressure agents, detergents, oxidation inhibitors, etc., which cause oils containing them to be severely corrosive to silver, the following may be mentioned: sulfurized lubricating oils, xanthate esters, chlorinated xanthate esters, dialkyl disulfides, sulfurized fatty oils, metal salts of reaction products of olefins and phosphorus pentasulfide, organic trisulfides, tetrasulfides and pentasulfides (e. g., parafiin wax polysulfide), polyvalent metal salts of organo-substituted acids of phosphorus (e. g., zinc hexyldithiophosphate), sulfurized olefins (e. g., sulfurized terpene), xanthic acid derivatives (e. g.. dibutyl xanthogen disulfide), etc.

Some of the above indicated additives are more vigorous in their attack on silver than others, and consequently such attack is more difficult to minimize. However, the silver protective agents are advantageously used even with the more act'ive sulfur additives.

The silver protective agents of this invention are also efiective in reducing attack on silver by the sulfur in lubricating oils derived from some of the crude oils characterized by their high sulfur content.

Although the silver protective agents are especially desirable and preferably used in combination with lubricating oils containing the polyvalent metal salts of organo-substituted thioacids of phosphorus (e. g., zinc cetyl phenyl dithiophosphate), they may be used in lubricating oils also containing such compounds as phenates (e. g., calcium cetyl phosphate), phenols (e. g., 2,6-di-tertiary-butyl-4-methyl phenol), phosphonates (e. g., calcium white oil phosphonate), thiophosphonates (e. g., calcium cetyl thiophosphonate), etc. The silver protective agents of this invention may be added to lubricating compositions containing other agents than sulfur-active agents, that'is, other agents which are advantageously present as oiliness agents, blooming agents, viscosity index improvers, pour point depressants, peptizing agents, etc.

For the purposes of the tests described hereinabove and below, the protective agents of this invention were incorporated in a mineral petroleum lubricating oil containing various sulfurcorrosive additives.

, Table I below presents'data of various compounds tested by the silver strip test. The various silver protective agents were added to a California solvent refined S. A. E. 30 paramnic base oil containing sulfurized calcium cetyl phenate; sulfurized diparafiin sulfide; calcium petroleum sulfonate, and zinc cetyl phenyl dithiophosphate.

Table II below presents silver strip test data of various compounds incorporated in a California solvent refined S. A. E. 30 parafiinlc base oil containing a calcium petroleum sulfonate. a sulfurized calcium cetyl phenate and zinc cetyl phenyl dithiophosphate.

Further silver strip tests were made by incorporating the protective agents of this invention in a California solvent refined S. A. E. 30 paraflinic base oil to which had been added calcium petroleum sulfonate, sulfurized diparaffin sulfide and a commercial oxidation inhibitor containing sulfurized olefins. The results of these tests are presented below in Table III.

Table III Amount of frotgcivel Tilei$trilp v gen se es ei t Protecme Agent in Lubricating Loss in Oil (Percent Milligrams by Wgt.)

1. None 93.0 2. 2-Meroapto 4,6,6-Trimethyl 'lhiazine 0.3 20. 1

Table IV presents data showing the eifectiveness of the compounds of this invention as protective agents in a California solvent refined S. A. E. 30 paraflinic base 011 containing calcium petroleum sulfonate, sulfurized diparafiin sulfide, a barium dithiophosphate, and trioctyl thiophosphate, which composite oil without the protective agent is extremely corrosive to silver.

Table IV I Amount of frotgcttlived lilver$ trip gen se est, t eight Fromm Agent in Lubricating Loss in Oil (Percent Milligrams by Wgt.)

1. None 852.1 2. 2 Mercapt0 4,6,6Trin1ethyl Thiazine 0.3 116. 9

In order to show further the effectiveness of the compounds of this invention as protective agents against sulfur corrosion," compounded oils were tested in a General Motors 4-71 engine. This engine has silver-plated wrist-pin bushings, a bore of 4.25 inches, 2. stroke of 5.0 inches, a compression ratio of 16 to 1, and is operated at a speed of 2,000 R. P. M., an oil sump temperature of 230 F., and a jacket temperature of 180 F.

The silver wrist-pin bushing is weighed before it is placed into position for a test run. In order to prevent scoring of the silver wrist-pin bushing while it is being inserted into the connecting rod, the silver wrist-pin itself is cooled with solid CO2 and the connecting rod eye is heated.v After the silver wrist-pin bushinghas been inserted, the temperature is allowed to reachv equilibrium.

After the silver wrist-pin bushing has been inserted for the test, the engine is run for 8 hours in order to break in the new wrist-pin bushing. The oil is then drained from the engine, fresh oil is added and the engine is run for an additional three-hour test period to make the. final engine adjustments, after which the oil is again drained and the test 011 added. The engine is then run for the full 200 hours at the conditions noted hereinabove.

The compounded oils to which the protective agents oi! this invention were added contained calcium cetyl phenyl dithiophosphate and zinc" cetyl phenyl dithiophosphate as the sulfur corrosive agents. Following the 200-hour test, the silver wrist-pin bushing was weighed to determine-the-loss of silver due to sulfur corrosion.

The results of the General Motors engine tests are presented below in Table. V.

Table V Amount of Protectivc Agent Added.

Appearance of Silver gg %g:

Protective Agent -Added. Wrist-Pin Bushing Y (Milligrams) The results presented in Table V show that the agents of this invention are remarkable in protecting the metals from attack by sulfur.

In order to show that the compounds oithis invention are not present in the lubricants for the-purpose of reducing the oxidation corrosion characteristics of the compounded oil, the test oil compounded as noted hereinabove was tested in an engine according to the LA-Test Method. described in pages 394-418 of the CRC Handbook compiled by the Coordinating Research Council, Inc. in 1946 and printed by the-J- J; Littleand; Ives Company. New York. This.te'st'is'-usedito determine the oxidation corrosiveness of the oils.

The L-4 procedure test engine is a stock 1942 Chevrolet engine, having a bore of 3.5 inches, a stroke of 3.75 inches and a compression ratio of 6.5 to 1. The rod bearings are babbitt, but with provisions for inserting cooper-lead bearings in place of the babbitt. For each test run, two

of the babbitt bearings were replaced with i weighed copper-lead inserts. In preparation for the test, the engine is flushed twice with uncompounded hydrocarbon lubricating oil (using. 4' quarts of the oil each time) by running the engine at a speed of 1500 R. P..M.- for 15 minutes At the end of the 20-hour test run, the copper leadbearing inserts are-washed free of oil, then weighed" to determine the weight lost. The

Table VI Base Oil Protective Agent Added ggggi gg Lead- Bearing b Insert (Milli- I y grams) v A 2-Mercapto4, 6, (i- Tri- 0.3 32

methyl Thiazine.

We claim: I

1. A sulfur-containing lubricating oil 'composi-j tion severely corrosive to silver, and a small. amount, sufiicient substantially to reduce the sulfur attack on silver of a 2-thiothiazinev selected from the group consisting of a Z-mercapt'othiazine and a zinc salt of a 2 mercaptothiazine, wherein said 2-mercaptothiazine contains. no more than 3 aliphatic radicals, said aliphatic radicals having no more than 8 carbon atoms.

2. Asuliur-containing lubricating oil'fcomp'os'i tion severely corrosive. to silver and a small amount, sufiicient substantially. to reduce the sulfur attack on silver of a'Z-mercaptothiazine.con taming. no more. than. 3 aliphatic radicals, said. aliphatic radicals having no. more than 8 carbon atoms.

3. The lubricatin oil composition of claim 2 whereinthe 2-mercaptothiazine. contains no more. than 3 methyl radicals.

4. A sulfur-containing, lubricating oil composition severely corrosive to silver and. a small amount sufiicient substantially to reduce the sulfur attack on silver of. a zinc salt of a 2-mercapto-v thiazine containing no more than 3 aliphatic. radicals, said aliphatic radicals having 'no more than 8 carbon atoms.

5. The lubricating oil composition of' claim 4 wherein said 2-mercaptothiazine contains no more than 3 methyl radicals.

6. The lubricating oil composition of claim 4- wherein said 2-mercaptothiazine is 2-inercapto- 4,6,6-trimethylthiazine.

7. A- sulfur-containing lubricating oilseverely.v corrosive to. silver, and a small amount. suflicient substantially to reduce the sulfur attack on silver, of 'a Z-mercapto-4,6,6-trimethyl thiazine.

WARREN LOWE. JAMES O. CLAYTON.

REFERENCES CITED The following references are of record in thefile of this patent:

UNITED STATES PATENTS Number Name Date 2,154,096 Loane Apr. 11, 1939 2,160,293 Shoemaker May 30, 1939 2,190,648 Cantrell Feb. 20, 1940 2,201,258 Busse May 21, 19.40. 2,293,237 Bartlett Aug. 18, 1942 2,318,629 Prutton May 11, 1943' 2,414,257 Evans et al Jan. 14, 1947 2,440,095 Janes Apr. 20, 1948- 

1. A SULFUR-CONTAINING LUBRICATING OIL COMPOSITION SEVERELY CORROSIVE TO SILVER, AND A SMALL AMOUNT, SUFFICENT SUBSTANTIALLY TO REDUCE THE SULFUR ATTACK ON SILVER OF A 2-THIOTHIAZINE SELECTED FROM THE GROUP CONSISTING OF A 2-MERCAPTOTHIAZINE AND A ZINC SALT OF A 2-MERCAPTOTHIAZINE, WHEREIN SAID 2-MERCAPTOTHIAZINE CONTAINS NO MORE THAN 3 ALIPHATIC RADICALS, SAID ALIPHATIC RADICALS HAVING NO MORE THAN 8 CARBON ATOMS, 